Process of manufacturing cast steel marine propellers

ABSTRACT

A tenacious cast steel, is used for manufacturing propellers, and has essentially the following composition: C: between about 0.03-0.07% Cr: between about 10-14% Ni: between about 5-7% Co: between about 3-5% Mo: between about 1.0-2.5% Si: not more than about 0.8% Mn: not more than about 1.2% and IMPURITIES, THE BALANCE BEING Fe, all percentages being by weight on total composition. In the marine propellers, a portion of the nickel content of this cast steel may be replaced by copper. The copper amount, however, should not exceed 3% by weight and the ratio of copper to nickel should be about 1:1. The process produces martensite steels having therein precipitates of molybdenum compounds which reinforce the cast steel propellers improving ductility toughness over conventional cast steels.

United States Patent Oda et al.

[ 1 Oct. 28, 1975 PROCESS OF MANUFACTURING CAST STEEL MARINE PROPELLERS[73] Assignee: Mitsubishi Jukogyo Kabushiki Kaisha, Japan [22] Filed:Oct. 5, 1972 [21] Appl. No.: 295,362

Related US. Application Data [63] Continuation-impart of Ser. No.80,452, Oct. 13, 1970, abandoned, which is a continuation-impart of Ser.No. 884,452, Decv 12, 1969, abandoned.

[52] US. Cl 148/3; 75/125; 75/128 B; 75/128 W; 148/37 [51] Int. Cl. C2ld9/00; C22c 39/26 [58] Field of Search 148/3, 37; 75/128 B [56]References Cited UNITED STATES PATENTS 2,499,860 3/1950 Hansen 148/32,557,971 6/1951 Jacklin 2,783,169 2/1957 Morgan..... 3,154,412 10/1964Kasak 3,192,073 6/1965 .lominyr. 3,278,298 6/1974 Perry 3,650,845 3/1972Ota 75/128 B 3,661,658 5/1972 Ota 148/3 Primary Examiner-L. DewayneRutledge Assistant Examiner-Arthur J. Steiner Attorney, Agent, orFirmMcG1ew & Tuttle [57] ABSTRACT A tenacious cast steel, is used formanufacturing propellers, and has essentially the following composition:

C: between about 0.03-0.07%

Cr: between about 10-14% Ni: between about 5-7% Co: between about 35%Mo: between about 1.02.5%

Si: not more than about 0.8%

Mn: not more than about 1.2% and impurities, the balance being Fe, allpercentages being by weight on total composition.

In the marine propellers, a portion of the nickel content of this caststeel may be replaced by copper. The copper amount, however, should notexceed 3% by weight and the ratio of copper to nickel should be about1:1. The process produces martensite steels having therein precipitatesof molybdenum compounds which reinforce the cast steel propellersimproving ductility toughness over conventional cast steels.

10 Claims, 2 Drawing Figures PROCESS OF MANUFACTURING CAST STEEL MARINEPROPELLERS REFERENCE TO PRIOR APPLICATIONS This is acontinuation-in-part of pending application Ser. No. 80,452, filed onOct. 13, 1970, which in turn is a continuation-in-part of applicationSer. No. 884,452, filed on Dec. 12, 1969 both of which are nowabandoned.

FIELD OF THE INVENTION The invention relates to manufacture of caststeel propeller constructions for marine use and to the cast steelmarine propellers produced thereby.

BACKGROUND INFORMATION AND PRIOR ART In recent years, ships, such astankers, have been constructed in ever increasing dimensions. This inturn has necessitated the construction of large size propellers orscrews. The increased size of the propellers has, of course, resulted inheavier propellers, to wit, propellers of greater weight. The weightincrease of a propeller in turn causes a number of difficult problems.'The heavier the propeller, the more material for its construction has tobe used, which in turn increases the costs. Accordingly, the nature ofthe material to be used for large size propeller constructions is ofconsiderable interest and emphasis has been placed on relativelyinexpensive materials. Further factors, such as power loss for driving alarge size propeller and difficulties in designing suitable sternstructures for such propellers, have to be considered.

With the view to overcoming these inherent difficulties, attempts havebeen made to construct large size propellers from alloy steelcompositions which are relatively lightweight, so as to decrease theweight of the final propeller, and which, at the same time, arerelatively inexpensive while having satisfactory mechanical properties.

To this end, it has previously been suggested to construct large sizepropellers from tenacious or tough cast steel which essentially consistsof not more than 0.25% of carbon, not more than 1.0% of silicon, notmore than 3.0% of manganese, between about 5 to 20% of chromium, l to 8%of cobalt, 0.5 to 7% of molybdenum and/or tungsten, not more than 8% ofnickel and/or not more than 4% of copper, the balance being iron.(Unless otherwise indicated in this specification, all parts andpercentages are by weight, based upon the total composition.)

Propellers constructed from this prior art material and used undercathodic protecting conditions have satisfactory properties andperformance characteristics, if the composition is gradually cooledafter casting from the austenitizing temperature and if coolinggenerally is effected gradually after subsequent heat treatments.However, this prior art cast steel composition has the disadvantage thatthe ductility of the composition significantly decreases during thecooling of the cast steel from the austenitizing temperature at acooling speed of 10C per minute or more. While this drawback perhaps isnot fatal for a satisfactory performance of propellers constructed fromthis composition, it is highly undesirable, because the decrease in theductility causes in turn a tendency 'for crack formation, particularlyduring welding operations. Thus, if parts made from such steel areheated to a temperature necessary for welding, which is required toconnect different parts or for repair purposes, the crack formationtendency is a very important factor which can only be counteracted byconsiderably lengthening the cooling time after heat treatments.

SUMMARY OF THE INVENTION It is the primary object of the presentinvention to overcome the aforesaid disadvantages of the prior artmethods of producing cast steel large sized propeller constructionshaving less desirable properties such as inferior ductility toughness.Another object is to provide a superior marine propeller of cast steelwhich is devoid of a tendency for crack formations.

A further object of the invention is to provide anovel cast steel marinepropeller construction which has superior mechanical properties, isrelatively inexpensive and of relatively low weight.

It is also an object of the invention to provide a process for making asteel composition for marine propellers which preserves its superiorductility characteristics without deterioration of other properties,even if the steel composition is cooled rapidly from the austenitizingtemperature or after subsequent heat treatments.

A still further object of the invention is to provide a process formaking a steel composition for marine propellers, whose superiorductility characteristics are independent from the cooling speed afterthe steel composition is subjected to heat treatments, for example, uponreheating to the austenitizing temperatureafter casting. I

Briefly, according to the invention, a tenacious cast steel propellerfor marine use is manufactured with es-. sentially the followingcomposition:

C between about 0.030.07%

Cr between about 1014% Ni between about 57% Co between about 3-5% Mobetween about l.02.5%

Si not more than about 0.8% v

Mn not more than about 1.2% and impurities, the

balance being Fe, all of said percentages being by weight based on thetotal steel composition.

A portion of the nickel content in the aforesaid composition canadvantageously be replaced by copper. The copper content, however,should not exceed 3% and the ratio of copper to nickel should then beabout 1:1.

The cast steel of this invention is for the most part face-centeredcubic austenite matrix; at sufficiently high temperatures, most of thematrix changes to bodycentered cubic ferrite or martensite, and yieldsprecipitates of inter-metallic compounds consisting mainly of theinter-metallic compound of molybdenum, when the body-centered cubiclattice matrix is again heated to a temperature between 450 and 700C.The purpose of precipitating the inter-metallic compounds of molybdenumis that, if the cast steel is reinforced by theseintermetalliccompounds, the ductility toughness characteristics of this cast steelare maintained up to a higher strength than those of conventional caststeels, e.g., those reinforced by carbides.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specifica tion. For a better understanding of theinvention, its operating advantages and specific objects attained by itsuses, reference should be had to the accompanying drawings anddescriptive matter in which there are illustrated preferred embodimentsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a table indicating the chemical composition of cast steel testpieces A through F, while FIG. 2 is a table indicating the mechanicalproperties of the test pieces A through F of FIG. 1, after having beensubjected to the various heat treatments indicated in the table.

The test pieces A through D were prepared by melting 30 kg of therespective alloy in a basic high frequency melting furnace and castingthe composition in a sand mold. By contrast, test pieces E and F wereprepared by melting 5 tons of the respective alloy in a basic Heroultfurnace and then casting the material into ingots of 1 ton weight.

As can be seen from FIG. 2, the ductility of the test pieces B-l, C-1and D-l, which were cooled rapidly after casting and were allowed tostand in cast condition, is low, while that of the test piece, which wasreheated to the austenitizing temperature after casting, is much higherand independent from the cooling speed. The mechanical properties of thethus heat treated test pieces are thus improved if compared with thoseof known steels. It will be appreciated that although the test piecesrepresented in the tables have a specific composition embraced withinthe scope of percentage ranges mentioned hereinabove, other specificcompositions may be used, provided they fall within the indi cated limitvalues.

The amount of impurities should be such as not to negatively affect theproperties of the steel. The respective P and S contents should thuspreferably not exceed 0.03%. The carbon content in the composition has amarked influence on the properties of the steel, particularly due to thesimultaneous presence of nickel and copper. In a preferred embodiment,the carbon content should be about 0.05%, but excellent results aregenerally obtained if the indicated range of 0.3 to 0.07% is adhered to.As a general proposition, it is rather diffi cult exactly to control thecarbon content in the composition.

The nickel content should be within the range of 57%. If the nickelcontent is too low, then the ductility cannot be satisfactorilymaintained upon quenching the steel. On the other hand, if the nickelcontent is too high, the residual austenite content increases. Asstated, a portion of the nickel content, however, may be replaced bycopper, the latter however not to exceed 3%. This is so because, if thecomposition contains more than 3% of copper, then the stability of thesteel is negatively affected. The best results are obtained if thecopper content does not exceed 3% and the ratio of copper to nickel isabout 1:1.

In respect to the chromium content, relatively high amounts aredesirable, to wit, the chromium should be within the indicated ratio ofto 14%. Chromium contents outside the indicated range are undesirablebecause, again, the stability of steel may then be affected. Thechromium, however, similar to cobalt, has a lesser influence on thesteel characteristics than have the carbon and nickel.

The cobalt content should be within the indicated range of 3 to 5%. Ifthe cobalt content fluctuates too much, then the optimum ranges for thenickel and copper contents are affected.

Referring now to the molybdenum content, this may vary between theindicated range of 1.0 to 2.5%. The molybdenum significantly contributesto the strength characteristics of the material. If the molybdenum issignificantly higher than 2.5%, then it is difficult to maintain thedesired ductility by rapid cooling.

The silicon and manganese additions are required as the de-oxidizingelements in the steel making and may be incorporated in the indicatedproportions of not more than 0.8 and 1.2%, respectively.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. Method of making marine propellers which comprises a. forming analloy composition of tenacious cast steel comprising the followingelements by weight: i. from about 0.03 to about 0.07% carbon,

ii. from about 10 to about 14% chromium,

iii. from about 5 to about 7% nickel,

iv. from about 3 to about 5% cobalt,

v. from about 1.0 to 2.5% molybdenum,

vi. not more than about 0.8% silicon,

vii. not more than about 1.2% manganese,

viii. substantially the balance being iron;

b. casting the aforesaid alloy composition in the form of a marinepropeller construction;

0. reheating said cast marine propeller construction to theaustenitizing temperature after casting; and

d. cooling the so-obtained marine propeller construction ofsubstantially martensite steel having improved ductility, tensilestrength and resistance to cracking at welding temperatures.

2. Method of making marine propellers, according to claim 1, whichcomprises replacing a portion of the nickel with copper, said copperamounting to not more than 3%, the ratio of copper to nickel being about1:1.

3. Tenacious cast steel marine propeller formed from an alloycomposition consisting essentially of the following elements by weight:

i. from about 0.03 to about 0.07% carbon,

ii. from about 10 to about 14% chromium,

iii. from about 5 to about 7% nickel,

iv. from about 3 to about 5% cobalt,

v. from about 1.0 to about 2.5% molybdenum,

vi. not more than about 0.8% silicon,

vii. not more than about 1.2% manganese,

viii. substantially the balance being iron; said alloy composition beingcast in the form of a marine propeller construction, reheated to theaustenitizing temperature after casting, and thereafter cooled, wherebya marine propeller construction is obtained having improved ductility,tensile strength and resistance to cracking at welding temperatures.

4. Tenacious cast steel propeller formed from an alloy composition, asset forth in claim 3 wherein a portion of nickel is replaced withcopper, said copper amounting to not more than 3% by weight, the ratioof copper to nickel therein being about 1:1.

6 5. Marine propeller according to claim 4, in which 8. Marine propelleraccording to claim 4, in which said cast steel consists essentially of:said cast steel consists essentially of:

i. about 0.06% carbon, 1 i. about 0.06% carbon, ii. about 0.28% silicon,ii. about 0.34% silicon, iii. about 0.45% manganese, 5 iii. about 0.40%manganese,

iv. about 12.58% chromium,

v. about 1.91% molybdenum vi. about 4.62% nickel,

vii. about 4.21% cobalt, and

viii. about 1.85% copper and the balance iron. 10

6. Marine propeller according to claim 4, in which said cast steelconsists essentially of:

i. about 0.03% carbon,

ii. about 0.23% silicon,

iii. about 0.29% manganese,

iv. about 0.12% chromium,

v. about 2.20% molybdenum,

iv. about 12.6% chromium,

v. about 1.96% molybdenum,

vi. about 5.57% nickel,

vii. about 3.93% cobalt, and

viii. about 1.62% copper, and the balance iron.

9. Marine propeller according to claim 3, in which said cast steelconsists essentially of:

i. about 0.06% carbon,

ii. about 0.46% silicon,

iii. about 0.34% manganese,

iv. about 11.78% chromium,

about 455% nickel. v. about 1.90% molybdenum, vii. about 4.03% cobalt,and 1: about 591% mckeli and viii. about 1.95% copper, and the balanceiron. abotft 415% cobalt and the balance 7. Marine propeller accordingto claim 4, in which Marine Propeller accorfimg to Clam whlch said caststeel consists essentially of: Said Cast steel conslsts essentlally of:

i. about 0.06% carbon, about 005% carbon. ii. about 0.17% silicon, about046% Silicon, iii. about 0.50% manganese, about 037% manganese, iv.about 12.60% chromium, iv. about l2-0l% chromium, v. about 1.91%molybdenum, v. about 1.88% molybdenum, vi. about 5.55% nickel, vi. about5.94% nickel, and vii. about 4.48% cobalt, and vii. about 4.12% cobalt,and the balance iron. viii. about 1.90% copper, and the balance iron. 3

1. METHOD OF MAKING MARINE PROPELLERS WHICH COMPRISES A. FORMING ANALLOY COMPOSITION OF TENACIOUS CAST STEEL COMPRISING THE FOLLOWINGELEMENTS BY WEIGHT: I. FROM ABOUT 0.03 TO ABOUT 0.07% CARBON II. FROMABOUT 10 TO ABOUT 14% CHROMIUM, III. FROM ABOUT 5 TO ABOUT 7% NICKEL,IV. FROM ABOUT 3 TO ABOUT 5% COBALT, V. FROM ABOUT 1.0 TO 2.5%MOLYBDENUM, VI. NOT MORE THAN ABOUT 0.8% SILICON, VII. NOT MORE THANABOUT 1.2% MANGANESE, VIII. SUBSTANTIALLY THE BALANCE BEING IRON, B.CASTING THE AFORESAID ALLOY COMPOSITION IN THE FORM OF A MARINEPROPELLER CONSTRUCTION, C. REHEATING SAID CAST MARINE PROPELLERCONSTRUCTION TO THE AUSTENITIZING TEMPERATURE AFTER CASTING, AND D.COOLING THE SO-OBTAINED MARINE PROPELLER CONSTRUCTION OF SUBSTANTIALLYMARTENSITE STEEL HAVING IMPROVED DUCTILITY, TENSIL STRENGTH ANDRESISTANCE TO CRACKING AT WELDING TEMPERATURES,
 2. Method of makingmarine propellers, according to claim 1, which comprises replacing aportion of the nickel with copper, said copper amounting to not morethan 3%, the ratio of copper to nickel being about 1:1.
 3. TENACIOUSCAST STEEL MARINE PROPELLER FORMED FROM AN ALLOY COMPOSITION CONSISTINGESSENTIALLY OF THE FOLLOWING ELEMENTS BY WEIGHT: I. FROM ABOUT 0.03 TOABOUT 0.07% CARBON, II. FROM ABOUT 10 TO ABOUT 14% CHROMIUM, III. FROMABOUT 5 TO ABOUT 7% NICKEL, IV. FROM ABOUT 3 TO ABOUT 5% COBALT, V. FROMABOUT 1.0 TO ABOUT 2.5% MOLYBDENUM, VI. NOT MORE THAN ABOUT 0.8%SILICON, VII. NOT MORE THAN ABOUT 1.2% MANGANESE, VIII. SUBSTANTIALLYTHE BALANCE BEING IRON, SAID ALLOY COMPOSITION BEING CAST IN THE FORM OFA MARINE PROPELLER CONSTRUCTION, REHEATED TO THE AUSTENITIZINGTEMPERATURE AFTER CASTING, AND THEREAFTER COOLED, WHEREBY A MARINEPROPELLER CONSTRUCTION IS OBTAINED HAVING IMPROVED DUCTILITY, TENSILESTRENGTH AND RESISTANCE TO CRACKING AT WELDING TEMPERATURES. 4.Tenacious cast steel propeller formed from an alloy composition, as setforth in claim 3 wherein a portion of nickel is replaced with copper,said copper amounting to not more than 3% by weight, the ratio of copperto nickel therein being about 1:1.
 5. Marine propeller according toclaim 4, in which said cast steel consists essentially of: i. about0.06% carbon, l ii. about 0.28% silicon, iii. about 0.45% manganese, iv.about 12.58% chromium, v. about 1.91% molybdenum vi. about 4.62% nickel,vii. about 4.21% cobalt, and viii. about 1.85% copper and the balanceiron.
 6. Marine propeller according to claim 4, in which said cast steelconsists essentially of: i. about 0.03% carbon, ii. about 0.23% silicon,iii. about 0.29% manganese, iv. about 0.12% chromium, v. about 2.20%molybdenum, vi. about 4.55% nickel; vii. about 4.03% cobalt, and viii.about 1.95% copper, and the balance iron.
 7. Marine propeller accordingto claim 4, in which said cast steel consists essentially of: i. about0.06% carbon, ii. about 0.17% silicon, iii. about 0.50% manganese, iv.about 12.60% chromium, v. about 1.91% molybdenum, vi. about 5.55%nickel, vii. about 4.48% cobalt, and viii. about 1.90% copper, and thebalance iron.
 8. Marine propeller according to claim 4, in which saidcast steel consists essentially of: i. about 0.06% carbon, ii. about0.34% silicon, iii. about 0.40% manganese, iv. about 12.6% chromium, v.about 1.96% molybdenum, vi. about 5.57% nickel, vii. about 3.93% cobalt,and viii. about 1.62% copper, and the balance iron.
 9. Marine propelleraccording to claim 3, in which said cast steel consists essentially of:i. about 0.06% carbon, ii. about 0.46% silicon, iii. about 0.34%manganese, iv. about 11.78% chromium, v. about 1.90% molybdenum, vi.about 5.91% nickel, and vii. about 4.15% cobalt, and the balance iron.10. Marine propeller according to claim 3, in which said cast steelconsists essentially of: i. about 0.05% carbon, ii. about 0.46% silicon,iii. about 0.37% manganese, iv. about 12.01% chromium, v. about 1.88%molybdenum, vi. about 5.94% nickel, and vii. about 4.12% cobalt, and thebalance iron.